vmwgfx: add dumb ioctl support

commit 5e1782d224c79b26ab7d5c31e3f87657000714fb upstream.

Testing and works with the -modesetting driver,

Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>